Chief Inspector Andy Lemon thanked the postal workers for spotting the suspicious letter before it reached him, and described it as an attempt to hurt or kill multiple officers in his station. He said it wasn't clear which specific IRA splinter group was behind the bomb.

British Army experts dismantled the device during a security operation that snarled traffic for several hours in Strabane, a predominantly Irish Catholic town that is a power base for several IRA factions in the British territory. Lemon is the town's police commander and the most senior officer to be targeted with a bomb in two decades.

"As police officers we are targets, and I would be quite high profile within Strabane," Lemon said. "I do not believe this is a personal attack but more a general attack on the police. Because I am area commander, a lot of mail would come into the police station addressed to myself, but I do not open any of it. That is done by other members of staff. So this was an attempt to kill or injure police."

The major IRA faction, the Provisionals, renounced violence and disarmed in 2005 after killing 1,775 people, including about 300 police officers, during a failed 1970-1997 campaign to force Northern Ireland out of the United Kingdom. But several breakaway factions, including at least two with members in Strabane, still mount occasional attacks. No group claimed responsibility for the intercepted letter bomb.

Today's IRA remnant hopes to undermine public support for Northern Ireland's Catholic-Protestant government, a 6-year-old coalition that has braved a series of security crises, and make it as hard as possible for police to operate in predominantly Catholic areas.

Government leaders denounced the Strabane bomb and appealed to its residents to help police identify those responsible. Such statements are considered politically significant because the Catholic deputy leader of the government, Martin McGuinness, was once a senior Provisional IRA commander hostile to the police.

"The individuals behind this need to be brought to justice as actions like this have no place in society and those responsible have nothing positive to offer," said the joint statement from McGuinness and First Minister Peter Robinson, a Protestant. "This was not just a planned attacked on a police officer but also on the postal workers involved and society as a whole. Violence plays no part in our future."

IRA splinter groups have killed two off-duty soldiers, two policemen and a prison officer since 2009.

Irish media typically try to label each faction distinctively, but last year three of those groups - the Real IRA, Oglaigh na hEireann, and Republican Action Against Drugs - announced they had united under one command and wished simply to be described as "the IRA." A fourth group, the Continuity IRA, has retained its own brand.